So now that we understand just what
exactly happens when a volcanic eruption
occurs, we can take a deeper look at the
meaning behind it all. Just what are
the effects of volcanic eruptions on global
climate change?
And now, the moment we have all been
waiting for…
1)
2)
3)
The Ozone Effect
The Greenhouse Effect
The Haze Effect
The diagram opposite illustrates the ozone layer.
The region in blue illustrates the hole of ozone
depletion, which extended to a record 10.5
million square miles on September 19th, 1998.
1)
The Ozone Effect
Within the earth’s atmosphere, there exists a sensitive state of equilibrium
between ozone (O3) and oxygen molecules (O2). Ozone molecules (O3) are
produced by intense sunlight in the stratosphere (above 12 kilometres), which
breaks down normal oxygen molecules (Os) into two highly reactive oxygen
Molecules (O). The O atoms are then supposed to quickly combine with O2
present to form O3. However, recently, the ozone layer has been depleted to
such an extent that a hole has been discovered in the stratosphere over
Antarctica.
The Role of Volcanoes
When volcanoes erupt, they produce large amounts of HCl (Hydrochloric Acid).
It is well known that HCl reacts with Ozone and thus damages the ozone layer.
Recent findings, however, now seem to suggest that volcanic HCl never in fact
reaches the ozone layer and thus it’s impact is no longer thought to be direct,
but instead that of catalysis. Scientists now believe that the HCl produced by
volcanic eruptions provides surfaces upon which the chemical reactions between
Ozone and human-generated CFC’s, example from aerosol cans of products such as
deodorants. These Chluorofluorocarbons contain bromine and chlorine
compounds which react with ozone and thus create the holes in the ozone layer. Thus
Volcanic eruptions in this case merely play an indirect role in ozone depletion.
Effect on Global Climate Change
With the ozone depleted it allows extra U.V. light to enter the earth’s
atmosphere. This causes an increased melting in the polar ice-caps which in
turn leads to rise in sea level. It also increases the sea level temperature. Thus
The ozone depletion situation puts great risk on the global ocean current
systems.
The website by Bruce C. Douglas
(http://www.agu.org/revgeophys/dougla01/dougla01.html) summarises the
impacts that global sea level rise would incur:
“Physical effects of sea level rise into 5 categories. These are inundation of
low-lying areas, erosion of beaches and bluffs, salt intrusion into aquifers and
surface waters, higher water tables, and increased flooding and storm damage.
All of these effects have important impacts, but I shall consider only the first
two in this review because they have had and are continuing to have very
dramatic impacts on coastal regions worldwide”
Other Impacts:
The ozone layer is responsible for protecting the earth from the dangerous ultra-violet (U.V.) radiation emitted from the
sun. This ultra-violet radiation is responsible for the increase in skin disease, for example melanoma. These diseases
would be most common in countries such as Australia and South Africa where the climate is warmer and the ozone
layer is more depleted.
What happens is that the ultra-violet radiation causes the DNA present in the skin cells to mutate. According to
Campbell et al (2002). Biology. Bejamin Cummings, San Francisco carcinogens, such as U.V. light, cause the DNA in
cells to divide in an out-of-control manner, i.e. U.V. light causes cancer. Although melanoma only accounts for about
4% of all skin cancer cases, it causes the most skin-cancer-related deaths.
For more information on melanoma, the following websites is recommended:
1)
2)
http://www.melanoma.com/melanoma/isMelanoma/index.jsp
http://www.mpip.org/
Example
An example of the most dramatic ozone loss as a result of a volcanic
eruption occurred in 1991. In this year, the combined eruptions of Mt
Pinatubo (in the Phillipines) and Mt Hudson (in Chile) showed a 15-20%
ozone loss at high latitudes and a greater than 50% loss over the Antarcic.
The diagram opposite shows the location of
Mt Hudson in Chile,
South America.
2) The Greenhouse Effect
DIAGRAM I DREW OF SUN/EARTH/ETC
GREENHSE EFFECT
This diagram drawn by Joanna Wakely describes the impact of the ozone layer
and other greenhouse gases collectively have on the retaining of heat energy
received from the sun.
These gases prevent the heat (that enters our atmosphere from the sun) from
escaping and without these, earth would be about 30 degrees colder than it is
at present life as we know it would not exist.
So What’s the Problem?
The problem that earth is currently facing, is that recent human activities are
enhancing the natural greenhouse effect, so that more of the infa-red radiation
emitted by the earth’s surface is being trapped. So in relation to the
greenhouse analogy, it is as if the atmosphere around the earth acts like a
glass pane. The glass pane allows the heat in but only a certain amount of the
heat is permitted to be radiated back out. With the increase in the greenhouse
gases mentioned on the previous pages however, the “glass pane” is
effectively thickening.
On the right-hand side of the page is an
Illustration relating the greenhouse effect
to fuel emissions of cars based on human
Impact on the greenhouse effect, another
Contributing factor.
The Table Below Illustrates Some of the Greenhouse Gases, Some of their
Sources, %of Total Emissions in 2001 and the Length of Time Each Gas
Remains in Earth’s Atmosphere From the Time of Emission
GAS
% TOTAL
EMISSIONS,
2001
SOURCE
LIFE SPAN
Carbon dioxide (CO2)
Fossil fuels,
deforestation, soil
destruction
Methane (CH4)
Cattle, biomass, rice
paddies, gas leaks,
mining, termites
9.3%
7-10 years
Nitrous oxide (N2O)
Fossil fuels, soil
cultivation,
deforestation
5.2%
140-190 years
Chlorofluorocarbons
(CFCs 11 and 12),
HFCs, PFCs and
Sulfur Hexaflouride
Refrigeration, air
conditioning,
aerosols, foam
blowing, solvents
1.7%
65-110 years
Ozone and other trace
gases
Photochemical
processes, cars,
power plants,
solvents
Less than 0.5%
Hours to days in upper
troposphere
83.8 %
500 years
What is the Greenhouse Effect?
The earth is heated by the sun’s rays which enter the atmosphere
as Infa-Red light. All this heat reaches the earth’s surface except
for a very small portion which is radiated back out of our
atmosphere.
The greenhouse gases present in our atmosphere include:
1)
2)
3)
4)
5)
6)
Methane (CH4)
Water Vapour (H2O)
Carbon Dioxide (CO2)
Nitrous Oxides
CFC’s (and their Replacements)
Ozone (03)
The diagram opposite is a cartoon showing how
the greenhouse effect could someday in the notso-distant future, cause the polar ice-caps to melt.
How Greenhouse Effect is Related to Volcanic Eruptions
The Greenhouse Effect is mainly caused by emission of carbon dioxide (CO2)
Released when burning fossil fuels. In fact, in contrast with this, the impact of
volcanic eruptions is really rather insignificant.
This is illustrated in the figures. Each year about 110 million tonnes of CO2
Are produced as a direct result of volcanic activity. This may seem like a lot but
compare it to the billion tonnes produced each year as a consequence of
human activities and the point is made clear.
Global warming is of great concern, especially since the 1980’s increase of
travel and privately-owned automobiles.
3)The Haze Effect
Volcanic Eruptions enhance the haze effect to a greater extent than the
greenhouse effect.
The Answers.com website (link given below) defines a haze as follows:
http://www.answers.com/haze&r=67
A thick, heavy atmospheric condition offering reduced visibility because of the
presence of suspended particles: brume, fog, mist, murk, smaze.
The Haze Effect is caused by sulfurous gases emitted by volcanoes during
eruption. The process which occurs is that the sulfur combines with the water
vapour present in our stratosphere to form dense of tiny sulfuric acid droplets.
The particles absorb solar radiation and scatter it back into space. These
droplets take several years to settle out, however, once this has occurred, they
are capable of decreasing the troposphere temperatures through this process.